While most shows' pilots air as their first episode, some shows get a do-over to make creative changes, improve production, or appease the network. We look at some of the pilots that didn't make it and how the shows changed.

Buffy the Vampire Slayer (Riff Regan vs. Alyson Hannigan)

What they changed: Joss Whedon financed the original pilot himself, formatting it as a half-hour episode. It is, for the most part, a shortened version of "Welcome to the Hellmouth," but with different casting. The role of the Sunnydale library was played by Torrance High School's library — a much larger and airier room than the cramped Hellmouth library we've come to know and love, with a handy second floor for showing off those Buffy backflips. Instead of Ken "Hyena Chow" Lerner as Principal Flutie, we get a much more straightlaced interpretation from character actor Stephen Tobolowsky. But perhaps the biggest difference is in the role of Willow. Instead of Alyson Hannigan, the geeky witch was originally played by Riff Regan.

How might the series have been different? Flutie probably would have still ended up in the stomachs of his students, but the Scooby Gang might have never been the same. Regan's Willow was a sweet doormat, but she didn't have quite the neurotic, eager-to-please quality Hannigan brought to the role. Incidentally, it wasn't the first time Hannigan replaced an actress after the filming of a show's initial pilot. In 1989, she took over the role of Jessie Harper in the fantasy sitcom Free Spirit.

Unaired Pilot with Stephen Tobolowsky and Riff Regan:

Official Pilot — "Welcome to the Hellmouth:"

Dollhouse (Joss Whedon vs. Fox)

What they changed: The premise and the characters are the same, but the stories unfold in a rather different way. We're initially introduced to Echo through a trio of very different engagements: one philanthropic, one as a revenge date, and one where she talks down gangsters in Espagnol. Boyd is already Echo's handler, and Topher has already caught onto Echo's bison-like grouping with Victor and Sierra. Agent Paul Ballard also comes face-to-face with Echo in the original pilot...when Topher programs Echo to kill him.

How might the series have been different? The original pilot played more as the start of a noir series than as a proof-of-concept for an engagement-of-the-week serial (which is what the official pilot "Ghost" suggests). We probably would have leaped to Dollhouse's underlying plot more quickly, and spent more of the season focusing on Echo's emerging awareness. Plus, it seems the Dollhouse was originally going to be more hands on in addressing Ballard's investigation. We see some of that noir (and slightly more classically Whedonesque dialogue) in the original pilot clip below:

What they changed: The most readily obvious difference between the unaired pilot and what aired on Fox is that Tim Guinee, who played Tomin in Stargate SG-1, was originally cast as Sarah's jilted fiance Charley, but was replaced in the official pilot by Dean Winters. But more significant is a key change in the final scene. In official pilot, when Sarah Connor delivers her final voiceover, we see her caress her son's face before walking into her home. In the original pilot, we instead see her pulling a gun out of its hiding place while Cameron and John sit in the same room preparing their weapons, showing that Sarah's focus is on the coming war.

How might the series have been different? It's hard to say to what extent this change represents a shift in tone across the series, but we worried that it signaled a "wimpifying" of Sarah Connor, showing her vulnerability where it could have shown her strength and determination. You can scene the unaired scenes and their official pilot counterparts below:

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Life on Mars (US) (Sunny LA vs. Gritty NY)

What they changed: Pretty much whatever they could. The original pilot for the US adaptation of Life on Mars was thoroughly panned, and producers quickly moved the action from Los Angeles to New York (allowing for that Twin Towers shot), and recast several roles. Star Trek vet Colm Meaney was replaced by Harvey Keitel in the role of Gene Hunt and Gretchen Mol took over Rachelle Lefevre's role as Annie Norris (Lefevre might have experienced an unfortunate moment of deja vu when she was recently replaced in yet another role — as the vampire VIctoria in Eclipse). But beyond that, certain scenes from the original pilot were rewritten to more closely match the UK version, and made the scenes visually darker and more textured.

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How might the series have been different? It simply wouldn't have been as good. The original US pilot genericized the UK version, washing it of all character. By ultimately sticking closer to the source material, the US version of Life on Mars was able to echo its tone while creating a new mythology to explain Sam Tyler's predicament.

Scene from the Unaired Pilot:

Scene from the Official Pilot:

Star Trek (Christopher Pike vs. James T. Kirk)

What they changed: The original pilot "The Cage" was a completely episode from the official Star Trek pilot "Where No Man Has Gone Before," with an almost completely different Enterprise crew. In lieu of William Shatner's syncopated Captain Kirk, Jeffrey Hunter was set to helm the ship as Captain Christopher Pike, and Star Trek creator Gene Roddenberry's future wife, Majel Barrett, played his intellectual and rational second-in-command, known only as "Number One." Spock would be the sole crew member to make the transition from first pilot to official pilot, but even he would undergo some minor changes. The original pilot's Spock was known to smile and use human colloquialisms, while the final Spock inherited Number One's sense of cold, hard logic.

How might the series have been different? The basics of the Enterprise and the Federation would have remained largely the same (in fact, most of the footage from "The Cage" would be cannibalized for a later episode "The Menagerie"). But the dynamics of the crew would have been very different. Pike wasn't the emotive adventurer Kirk would be, and he wasn't cast in as nearly sharp relief against either Spock or Number One. Plus, the original pilot's entirely caucasian cast was hardly the rainbow coalition that made the final version of Star Trek such a progressive piece of television.

Original Pilot — "The Cage:"

Official Pilot — "Where No Man Has Gone Before:"

Doctor Who (The Doctor from the 49th Century vs. The Doctor from Another Time

What they changed: The original episode of the first Doctor Who serial "An Unearthly Child" has the feel of a filmed dress rehearsal, but there were a few changes made beyond tightening the performances and improving production values. The Doctor and Susan both undergo costume changes — Susan into a more casual, less futuristic look and the Doctor from a modern suit to an Edwardian one — and the Doctor is much less gruff than in the original pilot. Also, in the original pilot, the Doctor and Susan talk specifically about being from the 49th Century, rather than the being from "another time, another world."

How might the series have been different? Aside from making the First Doctor outright hostile to his new companions instead of largely indifferent to them, the original pilot is a bit less mysterious about the Doctor and Susan's origins. If it had gone to air, it might have set the stage for a Doctor who is less coy and more forthcoming.

Segment from the Original Version:

Segment from the Official Version:

Heroes (Terrorists and Severed Limbs vs. An 8pm Timeslot

What they changed: The full version of the unaired Heroes pilot clocks in at 74 minutes, with a couple of plotlines that never made it into the final version. For example, DL appears as a prison inmate with a grudge against Nathan — the prosecutor who put him away. A childhood friend of Matt Parkman's is now a member of a terrorist cell and develops radiation-based powers, and his terrorist cell is responsible for the train wreck in Texas. Zachary Quinto had not yet been cast as Gabriel Gray, aka Sylar, but a shadowy figure named Paul Sylar meets with Mohinder. And, Isaac Mendez meets with a rather gruesome end: he handcuffs himself to a pipe to withdraw from heroin, but ends up sawing his own hand off instead, after which he promptly overdoses.

How might the series have been different? The original pilot suggests a somewhat darker, more violent vision for Heroes. With this as the pilot, we might have seen that brain-eating Sylar after all.

Lost in Space (Space Family Robinson vs. Dr. Smith and the Robot)

What they changed: In the official pilot, the Robinson family, Major Don West, and a B-9 Robot go into a space, only to be stranded far from home when a stowaway, Dr. Zachary Smith, sabotages the ship. By the second episode, the Robinsons managed to repair the ship so they could embark on lots of spacefaring adventures. The original pilot, though, is much more Swiss Family Robinson, with only the Robinson family and Don West — no Robot, no Smith — going into space, only to crash land on an alien planet. By the end of the pilot episode, they are still on the planet with no sign of them returning to space.

How might the series have been different? In addition to depriving us of the catchphrase "Danger, Will Robinson!" and the character audiences loved to hate, Lost in Space would have been a very different species of show, with the focus on how the family survives on an alien planet rather than following their far-flung adventures in space.

Original Pilot — "No Place to Hide:"

Official Pilot — "The Reluctant Stowaway:"

Of course, there are plenty of other shows reshot all or portions of their pilots. Birds of Prey, Smallville, True Blood, and Bionic Woman all recast key roles after shooting their pilots, while shows like Nickelodeon's Space Cases had only "proof of concept" pilots and had to film entirely new episodes with improved sets, makeup, special effects, and hair: